CALX INCREASING THE SUPPLY OF CARBON. 251 



actions of calcareous earth in soils, Dr. Wight proceeded to say 

 that in his consideration of the subject "it became a question of 

 deep interest to determine what was the peculiar influence of lime 

 in the process of vegetation ; and for this purpose the following 

 experiments were instituted. Seeds of wheat, resting upon moist- 

 ened cotton, were first placed in glasses of water, and thus allowed 

 to germinate. When two or more plants had put forth five roots, 

 which is their complement, or an equal number, taking especial 

 care that those experimented with should have an equal number 

 of roots, this being the test of their being equally healthy, they 

 were immediately transferred, half of them to vessels of pure rain- 

 water, the other half to vessels of rain-water in which a small portion 

 of the hydrate of lime [or slaked quick lime] had been dissolved. 



"As soon as the first leaf had attained sufficient length, they 

 were introduced under separate receivers, and supplied with car- 

 bonic acid. It was soon apparent, however, that the plants growing 

 in the pure rain-water threw off more oxygen than the others, 

 though the difference was slight. The experiment was repeated 

 with the other leaves, as they were successively unfolded, but with 

 no better success. 



" The carbonate of lime, or lime in the state it is found as a 

 natural production, was now substituted for the hydrate. Select- 

 ing the thin pellicle which collects upon lime-water, and reducing 

 it to a fine powder, as much was previously dissolved in the rain- 

 water in which half of the plants were to grow as could be, by 

 brisk agitation for a few minutes in a closed bottle. The plants to 

 be experimented with being always transferred from the glasses as 

 soon as it was perceived that they had an equal number of roots. 

 Previous to the period at which plants become dependent upon ex- 

 terior influences, the effect of the carbonate of lime was rather to 

 retard than to quicken the decomposing process ; but generally, by 

 the time the second leaf had fully unfolded itself, and always in 

 the case of the third, the greater resistance offered to the touch, 

 and the deeper and more polished tint of green, inspired anticipa- 

 tions of a successful result. When introduced under the receiver, 

 and supplied with carbonic acid, these anticipations were more than 

 fully realized the plants growing in rain-water in which carbo- 

 nate of lime had been previously dissolved, giving off two, three, 

 and sometimes four volumes of oxygen to one disengaged by those 

 growing in pure rain-water ; and for every volume of oxygen 

 emitted, an equal quantity of carbonic acid disappeared from the 

 jar containing it. These experiments were frequently and care- 

 fully repeated with the other plants cultivated in this latitude, 

 until it seemed to be fully ascertained that the influence of the 

 carbonate of lime in the process of vegetable nutrition consists in 

 increasing the action of plants upon the light in so modifying 



